4 * Copyright (C) 1991, 1992, 1993 Linus Torvalds
8 * head.S contains the 32-bit startup code.
10 * NOTE!!! Startup happens at absolute address 0x00001000, which is also where
11 * the page directory will exist. The startup code will be overwritten by
12 * the page directory. [According to comments etc elsewhere on a compressed
13 * kernel it will end up at 0x1000 + 1Mb I hope so as I assume this. - AC]
15 * Page 0 is deliberately kept safe, since System Management Mode code in
16 * laptops may need to access the BIOS data stored there. This is also
17 * useful for future device drivers that either access the BIOS via VM86
22 * High loaded stuff by Hans Lermen & Werner Almesberger, Feb. 1996
27 #include <linux/init.h>
28 #include <linux/linkage.h>
29 #include <asm/segment.h>
32 #include <asm/processor-flags.h>
33 #include <asm/asm-offsets.h>
39 * 32bit entry is 0 and it is ABI so immutable!
40 * If we come here directly from a bootloader,
41 * kernel(text+data+bss+brk) ramdisk, zero_page, command line
42 * all need to be under the 4G limit.
46 * Test KEEP_SEGMENTS flag to see if the bootloader is asking
47 * us to not reload segments
49 testb $(1<<6), BP_loadflags(%esi)
53 movl $(__BOOT_DS), %eax
60 * Calculate the delta between where we were compiled to run
61 * at and where we were actually loaded at. This can only be done
62 * with a short local call on x86. Nothing else will tell us what
63 * address we are running at. The reserved chunk of the real-mode
64 * data at 0x1e4 (defined as a scratch field) are used as the stack
65 * for this calculation. Only 4 bytes are needed.
67 leal (BP_scratch+4)(%esi), %esp
72 /* setup a stack and make sure cpu supports long mode. */
73 movl $boot_stack_end, %eax
82 * Compute the delta between where we were compiled to run at
83 * and where the code will actually run at.
85 * %ebp contains the address we are loaded at by the boot loader and %ebx
86 * contains the address where we should move the kernel image temporarily
87 * for safe in-place decompression.
90 #ifdef CONFIG_RELOCATABLE
92 movl BP_kernel_alignment(%esi), %eax
98 movl $LOAD_PHYSICAL_ADDR, %ebx
101 /* Target address to relocate to for decompression */
102 addl $z_extract_offset, %ebx
105 * Prepare for entering 64 bit mode
108 /* Load new GDT with the 64bit segments using 32bit descriptor */
110 movl %eax, gdt+2(%ebp)
113 /* Enable PAE mode */
114 movl $(X86_CR4_PAE), %eax
118 * Build early 4G boot pagetable
120 /* Initialize Page tables to 0 */
121 leal pgtable(%ebx), %edi
123 movl $((4096*6)/4), %ecx
127 leal pgtable + 0(%ebx), %edi
128 leal 0x1007 (%edi), %eax
132 leal pgtable + 0x1000(%ebx), %edi
133 leal 0x1007(%edi), %eax
135 1: movl %eax, 0x00(%edi)
136 addl $0x00001000, %eax
142 leal pgtable + 0x2000(%ebx), %edi
143 movl $0x00000183, %eax
145 1: movl %eax, 0(%edi)
146 addl $0x00200000, %eax
151 /* Enable the boot page tables */
152 leal pgtable(%ebx), %eax
155 /* Enable Long mode in EFER (Extended Feature Enable Register) */
158 btsl $_EFER_LME, %eax
161 /* After gdt is loaded */
168 * Setup for the jump to 64bit mode
170 * When the jump is performend we will be in long mode but
171 * in 32bit compatibility mode with EFER.LME = 1, CS.L = 0, CS.D = 1
172 * (and in turn EFER.LMA = 1). To jump into 64bit mode we use
173 * the new gdt/idt that has __KERNEL_CS with CS.L = 1.
174 * We place all of the values on our mini stack so lret can
175 * used to perform that far jump.
178 leal startup_64(%ebp), %eax
181 /* Enter paged protected Mode, activating Long Mode */
182 movl $(X86_CR0_PG | X86_CR0_PE), %eax /* Enable Paging and Protected mode */
185 /* Jump from 32bit compatibility mode into 64bit mode. */
193 * 64bit entry is 0x200 and it is ABI so immutable!
194 * We come here either from startup_32 or directly from a
196 * If we come here from a bootloader, kernel(text+data+bss+brk),
197 * ramdisk, zero_page, command line could be above 4G.
198 * We depend on an identity mapped page table being provided
199 * that maps our entire kernel(text+data+bss+brk), zero page
202 #ifdef CONFIG_EFI_STUB
204 * The entry point for the PE/COFF executable is efi_pe_entry, so
205 * only legacy boot loaders will execute this jmp.
214 call make_boot_params
221 ENTRY(efi_stub_entry)
227 /* EFI init failed, so hang. */
235 subq BP_pref_address(%rsi), %rax
236 add BP_code32_start(%esi), %eax
237 leaq preferred_addr(%rax), %rax
243 /* Setup data segments. */
252 * Compute the decompressed kernel start address. It is where
253 * we were loaded at aligned to a 2M boundary. %rbp contains the
254 * decompressed kernel start address.
256 * If it is a relocatable kernel then decompress and run the kernel
257 * from load address aligned to 2MB addr, otherwise decompress and
258 * run the kernel from LOAD_PHYSICAL_ADDR
260 * We cannot rely on the calculation done in 32-bit mode, since we
261 * may have been invoked via the 64-bit entry point.
264 /* Start with the delta to where the kernel will run at. */
265 #ifdef CONFIG_RELOCATABLE
266 leaq startup_32(%rip) /* - $startup_32 */, %rbp
267 movl BP_kernel_alignment(%rsi), %eax
273 movq $LOAD_PHYSICAL_ADDR, %rbp
276 /* Target address to relocate to for decompression */
277 leaq z_extract_offset(%rbp), %rbx
279 /* Set up the stack */
280 leaq boot_stack_end(%rbx), %rsp
287 * Copy the compressed kernel to the end of our buffer
288 * where decompression in place becomes safe.
291 leaq (_bss-8)(%rip), %rsi
292 leaq (_bss-8)(%rbx), %rdi
293 movq $_bss /* - $startup_32 */, %rcx
301 * Jump to the relocated address.
303 leaq relocated(%rbx), %rax
310 * Clear BSS (stack is currently empty)
313 leaq _bss(%rip), %rdi
314 leaq _ebss(%rip), %rcx
322 leaq _got(%rip), %rdx
323 leaq _egot(%rip), %rcx
333 * Do the decompression, and jump to the new kernel..
335 pushq %rsi /* Save the real mode argument */
336 movq %rsi, %rdi /* real mode address */
337 leaq boot_heap(%rip), %rsi /* malloc area for uncompression */
338 leaq input_data(%rip), %rdx /* input_data */
339 movl $z_input_len, %ecx /* input_len */
340 movq %rbp, %r8 /* output target address */
341 movq $z_output_len, %r9 /* decompressed length */
342 call decompress_kernel
346 * Jump to the decompressed kernel.
352 /* This isn't an x86-64 CPU so hang */
357 #include "../../kernel/verify_cpu.S"
364 .quad 0x0000000000000000 /* NULL descriptor */
365 .quad 0x00af9a000000ffff /* __KERNEL_CS */
366 .quad 0x00cf92000000ffff /* __KERNEL_DS */
367 .quad 0x0080890000000000 /* TS descriptor */
368 .quad 0x0000000000000000 /* TS continued */
372 * Stack and heap for uncompression
377 .fill BOOT_HEAP_SIZE, 1, 0
379 .fill BOOT_STACK_SIZE, 1, 0
383 * Space for page tables (not in .bss so not zeroed)
385 .section ".pgtable","a",@nobits